The rotor of the brushless motor is composed of two parts, the inside is a rotor core composed of silicon steel sheets, and the surface of the rotor core is pasted with permanent magnets. This is the surface-mounted permanent magnet structure.

Why do brushless motors need silicon steel sheets? Doesn't it mean that energized conductors can play a role in a magnetic field? Then why do you need silicon steel sheets?

Air is weakly permeable, but iron is permeable. The role of the silicon steel sheet is to guide the magnetic circuit of the magnet and form a loop. This requires the reluctance of the brushless motor (you can equate it as a resistance) smaller. But everyone has seen it, why are the stators and rotors formed piece by piece?

Do you know the principle of an induction cooker? Why does an iron pan heat up when placed on an induction cooker? In fact, this is because materials similar to iron are placed in a rapidly changing electromagnetic field (think about alternating current, that electricity is flying around instantly, Unlike direct current, which is always positive to negative, it will generate eddy current loss and generate heat, and the higher the frequency, the greater the heat generation. The silicon steel sheet is in the rotating magnetic field of the motor, and it encounters the same problem as the iron pan on the induction cooker. The solution is to add silicon to the steel and make it into a thin sheet. In theory, the thinner the silicon steel sheet is produced. The eddy current loss is smaller.